Dehydrocyclo-oligomerization is a process in which aliphatic hydrocarbons are reacted over a catalyst to produce aromatics and hydrogen and certain byproducts. This process is distinct from more conventional reforming where C6 and higher carbon number reactants, primarily paraffins and naphthenes, are converted to aromatics. The aromatics produced by conventional reforming contain the same or a lesser number of carbon atoms per molecule than the reactants from which they were formed, indicating the absence of reactant oligomerization reactions. In contrast, the dehydrocyclo-oligomerization reaction results in an aromatic product that typically contains more carbon atoms per molecule than the reactants, thus indicating that the oligomerization reaction is an important step in the dehydrocyclo-oligomerization process. Typically, the dehydrocyclo-oligomerization reaction is carried out at temperatures in excess of 260° C. using dual functional catalysts containing acidic and dehydrogenation components.
Aromatics, hydrogen, a C4+ non-aromatics byproduct, and a light ends byproduct are all products of the dehydrocyclo-oligomerization process. The aromatics are the desired products of the reaction as they can be utilized as gasoline blending components or for the production of petrochemicals. Hydrogen is also a desirable product of the process. The hydrogen can be efficiently utilized in hydrogen consuming refinery processes such as hydrotreating or hydrocracking processes. The least desirable product of the dehydrocyclo-oligomerization process is light ends byproducts. The light ends byproducts consist primarily of C1 and C2 hydrocarbons produced as a result of the cracking side reactions.
The uncoverted aliphatic hydrocarbons and a portion of cracking products from dehydrocyclodimerization reactor is separated, recovered and combined with the fresh feed, before entering the reactor. This recycle stream contains diolefins, mainly butadiene and C2-C4 olefins and aromatics. Olefins that are in the recycle stream are thermally converted to diolefins in the heater train. Some other products of the dehydrocyclo-oligomerization process are also not desirable. For example, di-olefins such as butadiene are known to cause pyrolytic coking of reactor internals and thus builds up pressure of reactors.
Accordingly, it is desirable to develop methods for saturating butadiene and butenes before the recycle stream is combined with the fresh feed and enters the reaction zone. Furthermore, other desirable features and characteristics of the present embodiment will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.